1. Field of the Invention
2. Discussion of Background Art
The present invention relates to a sensor unit for use in a system for monitoring the inside of a tire.
Conventionally, various proposals have been made for Tire Pressure Monitoring Systems (TPMS) which can monitor the inside pressures, etc. of tires attached to a vehicle. These kinds of pressure monitoring systems are constructed such that a sensor for detecting the inside pressure of a tire is fixed to a wheel. One example of a mounting structure of such pressure monitoring systems is disclosed in Japanese Laid-open Patent Application No. 2003-205716 (paragraphs [0015] to [0022]; FIGS. 1 and 3). In the sensor unit disclosed in Japanese Laid-open Patent Application No. 2003-205716, a base member is fixed in a predetermined position on the rim of a wheel by welding or screw-threaded engagement, followed by sandwiching a sensor body 3). In the sensor unit disclosed in Japanese Laid-open Patent Application No. 2003-205716, a base member is fixed in a predetermined position on the rim of a wheel by welding or screw-threaded engagement, followed by sandwiching a sensor body between the base member and another fixing member. Other proposals have been made such that the sensor body is integrally formed with a tire valve.
However, in the above sensor unit disclosed in Japanese Laid-open Patent Application No. 2003-205716, the base member has to be fixed, for example, by welding after positioning the base member on the rim of the wheel, which requires a time-consuming mounting operation. In cases where the base member is screw-threaded on the rim, it is necessary to prepare a dedicated wheel having screw holes or to form screw holes when an existing wheels is used, which also requires a time-consuming mounting operation.
To ease the mounting operation, it has been proposed that the base member be fixed to the rim with pressure sensitive adhesive. However, since pressure sensitive adhesive does not provide a sufficient adhesion force, the base member may be peeled off from the wheel by the centrifugal force caused by the rotation of the tire, causing the sensor body to be separated from the wheel.
Further, in the sensor unit of which sensor body is integrally formed with the tire valve, a load is focused around the tire valve, which is likely to cause the wheel to become unbalanced. For this reason, it is necessary to attach a weight for adjusting the wheel balance. Therefore, integrally forming the sensor body with the tire valve would disadvantageously deteriorate the maintenance.
In view of the above, it is an object of the present invention to provide a sensor unit which can realize a simple mounting operation of the sensor and which can enhance the long term reliability of adhesiveness.